/*
Copyright (c) 2007,2007 Elizeu Nogueira da R. Jr.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright notice, 
      this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright notice, 
      this list of conditions and the following disclaimer in the documentation 
      and/or other materials provided with the distribution.
    * Neither the name of the Elizeu Nogueira da R. Jr. nor the names of its 
      contributors may be used to endorse or promote products derived from this 
      software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


This package is based on HypersonicSQL, originally developed by Thomas Mueller.
and HSQLDB original developed by the HSQL Development Group
*/

package br.com.dreamsource.mobile.jmesql;

import br.com.dreamsource.mobile.jmesql.io.RandomAccessFile;
import br.com.dreamsource.mobile.jmesql.io.File;
import java.io.*;
import br.com.dreamsource.mobile.jmesql.exceptions.SQLException;

class Cache {
    
    private RandomAccessFile rFile;
    private final static int LENGTH = 1 << 14;
    private final static int MAX_CACHE_SIZE = LENGTH * 3 / 4;
    private Row		     rData[];
    private Row		     rWriter[];
    private Row		     rFirst;
    private Row		     rLastChecked;
    private String	     sName;
    private final static int MASK = (LENGTH) - 1;
    private int		     iFreePos;
    private final static int FREE_POS_POS = 16;
    private final static int INITIAL_FREE_POS = 32;
    private final static int MAX_FREE_COUNT = 1024;
    private CacheFree	     fRoot;
    private int		     iFreeCount;
    private int		     iCacheSize;

    Cache(String name) {
	sName = name;
    }
    
    void open(boolean readonly) throws SQLException {
	try {
	    boolean exists = false;
	    File    f = new File(sName);

	    if (f.exists() && f.length() > FREE_POS_POS) {
		exists = true;
	    }

	    rFile = new RandomAccessFile(sName, readonly ? "r" : "rw");

	    if (exists) {
		rFile.seek(FREE_POS_POS);

		iFreePos = rFile.readInt();
	    } else {
		iFreePos = INITIAL_FREE_POS;
	    }
	} catch (Exception e) {
	    throw Trace.error(Trace.FILE_IO_ERROR,
			      "error " + e + " opening " + sName);
	}
    }

    void flush() throws SQLException {
	try {
	    rFile.seek(FREE_POS_POS);
	    rFile.writeInt(iFreePos);
	    saveAll();
	    rFile.close();
	} catch (Exception e) {
	    throw Trace.error(Trace.FILE_IO_ERROR,
			      "error " + e + " closing " + sName);
	}
    }

    void shutdown() throws SQLException {
	try {
	    rFile.close();
	} catch (Exception e) {
	    throw Trace.error(Trace.FILE_IO_ERROR,
			      "error " + e + " in shutdown " + sName);
	}
    }

    void free(Row r, int pos, int length) throws SQLException {
	iFreeCount++;
	CacheFree n = new CacheFree();
	n.iPos = pos;
	n.iLength = length;
	if (iFreeCount > MAX_FREE_COUNT) {
	    iFreeCount = 0;
	} else {
	    n.fNext = fRoot;
	}
	fRoot = n;
	remove(r);
    }

    void add(Row r) throws SQLException {
	int       size = r.iSize;
	CacheFree f = fRoot;
	CacheFree last = null;
	int       i = iFreePos;

	while (f != null) {
	    if (Trace.TRACE) {
			Trace.stop();
	    }
		// first that is long enough
	    if (f.iLength >= size) {
		i = f.iPos;
		size = f.iLength - size;

		if (size < 8) {

		    // remove almost empty blocks
		    if (last == null) {
			fRoot = f.fNext;
		    } else {
			last.fNext = f.fNext;
		    }

		    iFreeCount--;
		} else {
		    f.iLength = size;
		    f.iPos += r.iSize;
		}

		break;
	    }

	    last = f;
	    f = f.fNext;
	}

	r.iPos = i;

	if (i == iFreePos) {
	    iFreePos += size;
	}

	int k = i & MASK;
	Row before = rData[k];

	if (before == null) {
	    before = rFirst;
	}

	r.insert(before);

	iCacheSize++;
	rData[k] = r;
	rFirst = r;
    }

    Row getRow(int pos, Table t) throws SQLException {
	int k = pos & MASK;
	Row r = rData[k];
	Row start = r;

	while (r != null) {
	    if (Trace.STOP) {
		Trace.stop();
	    }

	    int p = r.iPos;

	    if (p == pos) {
		return r;
	    } else if ((p & MASK) != k) {
		break;
	    }

	    r = r.rNext;

	    if (r == start) {
		break;
	    }
	}

	Row before = rData[k];

	if (before == null) {
	    before = rFirst;
	}

	try {
	    rFile.seek(pos);

	    int  size = rFile.readInt();
	    byte buffer[] = new byte[size];

	    rFile.readFully(buffer);

	    ByteArrayInputStream bin = new ByteArrayInputStream(buffer);
	    DataInputStream      in = new DataInputStream(bin);

	    r = new Row(t, in, pos, before);
	    r.iSize = size;
	} catch (IOException e) {
	    e.printStackTrace();

	    throw Trace.error(Trace.FILE_IO_ERROR, "reading: " + e);
	}

	// todo: copy & paste here
	iCacheSize++;
	rData[k] = r;
	rFirst = r;

	return r;
    }

    void cleanUp() throws SQLException {
	if (iCacheSize < MAX_CACHE_SIZE) {
	    return;
	}

	int count = 0, j = 0;

	while (j++ < LENGTH && iCacheSize + LENGTH > MAX_CACHE_SIZE
	       && (count * 16) < LENGTH) {
	    if (Trace.STOP) {
		Trace.stop();
	    }

	    Row r = getWorst();

	    if (r == null) {
		return;
	    }

	    if (r.bChanged) {
		rWriter[count++] = r;
	    } else {

		// here we can't remove roots
		if (!r.canRemove()) {
		    remove(r);
		}
	    }
	}

	if (count != 0) {
	    saveSorted(count);
	}

	for (int i = 0; i < count; i++) {

	    // here we can't remove roots
	    Row r = rWriter[i];

	    if (!r.canRemove()) {
		remove(r);
	    }

	    rWriter[i] = null;
	}
    }

    private void remove(Row r) throws SQLException {
	if (Trace.ASSERT) {
	    Trace.assert1(!r.bChanged);
	}

	if (r == rLastChecked) {
	    rLastChecked = rLastChecked.rNext;

	    if (rLastChecked == r) {
		rLastChecked = null;
	    }
	}

	// make sure rData[k] does not point here
	int k = r.iPos & MASK;

	if (rData[k] == r) {
	    Row n = r.rNext;

	    rFirst = n;

	    if (n == r || (n.iPos & MASK) != k) {
		n = null;
	    }

	    rData[k] = n;
	}

	// make sure rFirst does not point here
	if (r == rFirst) {
	    rFirst = rFirst.rNext;

	    if (r == rFirst) {
		rFirst = null;
	    }
	}

	r.free();

	iCacheSize--;
    }

    private Row getWorst() throws SQLException {
	if (rLastChecked == null) {
	    rLastChecked = rFirst;
	}

	Row r = rLastChecked;

	if (r == null) {
	    return null;
	}

	Row candidate = r;
	int worst = Row.iCurrentAccess;

	// algorithm: check the next rows and take the worst
	for (int i = 0; i < 6; i++) {
	    int w = r.iLastAccess;

	    if (w < worst) {
		candidate = r;
		worst = w;
	    }

	    r = r.rNext;
	}

	rLastChecked = r.rNext;

	return candidate;
    }

    private void saveAll() throws SQLException {
	if (rFirst == null) {
	    return;
	}

	Row r = rFirst;

	while (true) {
	    int count = 0;
	    Row begin = r;

	    do {
		if (Trace.STOP) {
		    Trace.stop();
		}

		if (r.bChanged) {
		    rWriter[count++] = r;
		}

		r = r.rNext;
	    } while (r != begin && count < LENGTH);

	    if (count == 0) {
		return;
	    }

	    saveSorted(count);

	    for (int i = 0; i < count; i++) {
		rWriter[i] = null;
	    }
	}
    }

    private void saveSorted(int count) throws SQLException {
	sort(rWriter, 0, count - 1);

	try {
	    for (int i = 0; i < count; i++) {
		rFile.seek(rWriter[i].iPos);
		rFile.write(rWriter[i].write());
	    }
	} catch (Exception e) {
	    throw Trace.error(Trace.FILE_IO_ERROR, "saveSorted " + e);
	}
    }

    private static final void sort(Row w[], int l,
				   int r) throws SQLException {
	int i, j, p;

	while (r - l > 10) {
	    i = (r + l) >> 1;

	    if (w[l].iPos > w[r].iPos) {
		swap(w, l, r);
	    }

	    if (w[i].iPos < w[l].iPos) {
		swap(w, l, i);
	    } else if (w[i].iPos > w[r].iPos) {
		swap(w, i, r);
	    }

	    j = r - 1;

	    swap(w, i, j);

	    p = w[j].iPos;
	    i = l;

	    while (true) {
		if (Trace.STOP) {
		    Trace.stop();
		}

		while (w[++i].iPos < p);

		while (w[--j].iPos > p);

		if (i >= j) {
		    break;
		}

		swap(w, i, j);
	    }

	    swap(w, i, r - 1);
	    sort(w, l, i - 1);

	    l = i + 1;
	}

	for (i = l + 1; i <= r; i++) {
	    if (Trace.STOP) {
		Trace.stop();
	    }

	    Row t = w[i];

	    for (j = i - 1; j >= l && w[j].iPos > t.iPos; j--) {
		w[j + 1] = w[j];
	    }

	    w[j + 1] = t;
	}
    }

    private static void swap(Row w[], int a, int b) {
	Row t = w[a];

	w[a] = w[b];
	w[b] = t;
    }

}
